1. Field of the Invention
This invention relates to the field of therapeutic drug delivery and more specifically, to gas-filled microspheres comprising a therapeutic compound. The invention further relates to methods for employing such microspheres as therapeutic drug delivery systems.
2. Background of the Invention
Targeted drug delivery means are particularly important where the toxicity of the drug is an issue. Specific drug delivery methods potentially serve to minimize toxic side effects, lower the required dosage amounts, and decrease costs for the patient. The present invention is directed to addressing these and/or other important needs in the area of drug delivery.
The methods and materials in the prior art for introduction of genetic materials to, for example, living cells is limited and ineffective. To date several different mechanisms have been developed to deliver genetic material to living cells. These mechanisms include techniques such as calcium phosphate precipitation and electroporation, and carriers such as cationic polymers and aqueous-filled liposomes. These methods have all been relatively ineffective in vivo and only of limited use for cell culture transfection. None of these methods potentiate local release, delivery and integration of genetic material to the target cell.
Better means of delivery for therapeutics such as genetic materials are needed to treat a wide variety of human and animal diseases. Great strides have been made in characterizing genetic diseases and in understanding protein transcription but relatively little progress has been made in delivering genetic material to cells for treatment of human and animal disease.
A principal difficulty has been to deliver the genetic material from the extracellular space to the intracellular space or even to effectively localize genetic material at the surface of selected cell membranes. A variety of techniques have been tried in vivo but without great success. For example, viruses such as adenoviruses and retroviruses have been used as vectors to transfer genetic material to cells. Whole virus has been used but the amount of genetic material that can be placed inside of the viral capsule is limited and there is concern about possible dangerous interactions that might be caused by live virus. The essential components of the viral capsule may be isolated and used to carry genetic material to selected cells. In vivo, however, not only must the delivery vehicle recognize certain cells but it also must be delivered to these cells. Despite extensive work on viral vectors, it has been difficult to develop a successfully targeted viral mediated vector for delivery of genetic material in vivo.
Conventional, liquid-containing liposomes have been used to deliver genetic material to cells in cell culture but have generally been ineffective in vivo for cellular delivery of genetic material. For example, cationic liposome transfection techniques have not worked effectively in vivo. More effective means are needed to improve the cellular delivery of therapeutics such as genetic material.